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EEE 314. Lecture 1.

Prepared by: Md. Itrat Bin Shams

Mr. Yeasir Arafat Contents

1. Drafting 2

2. Ratings of Electrical appliances 2

3. Description of Protecting Devices: 3

3.1 Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2 Fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.3 Circuit Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4. Grounding and Hazards 5

5. Illumination and lightning 6

5.1 Some definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2 Law of illumination . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3 Lamberts cosine law . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.4 Design of lighting scheme . . . . . . . . . . . . . . . . . . . . . . 8 5.5 Lighting Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.6 Outdoor lighting for general illumination . . . . . . . . . . . . . . 8 5.7 Method of lighting calculation . . . . . . . . . . . . . . . . . . . . 9

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1. Drafting

A reasonable amount of mathematical ability. Patience. An orderly mind. Imagination and ability to visualize. Ability to concentrate. Neatness.

2. Ratings of Electrical appliances

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3. Description of Protecting Devices

Main features of protecting devices: Sensitivity Selectivity Reliability Quickness: Non-interference with future expansion

3.1 Relays

Types of relays: (i) According to construction and principle of operation: Attracted Armature Type Solenoid Type Electro dynamic Type Induction type Thermal Type Moving coil type (ii) According to application: Over Voltage/ Over Current /Over Power Relay Under voltage/ Under Current /Under Power Relay Directional or Reverse Power Relay Directional or Reverse Current Relay Differential Relay Distance Relay (iii) According to Timing Characteristics: Instantaneous Relay Definite Time Lag Relay Inverse Time Lag Relay

3.2 Fuse

A fuse must fulfill following criteria: During normal operating conditions fuses must not have any effect over circuits. A fuse must sense a short circuit or overload. A fuse must open the circuit before any harm is caused to the system.

Figure 1

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Fuses can be classified as,

Edison Base Fuses Type S Fuses Cartridge-Type Fuses Ferrule-Type Fuses Knife Blade-Type Fuses

Figure 2

Figure 3

3.3 Circuit Breakers

Classification of Circuit Breakers: Electromagnetic-Type Circuit Breaker Thermal-Type circuit breaker

Figure 4

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Figure 5

4. Grounding and Hazards

a. Grounding by the electric utility b. Grounding by the electrician

1. Fire Hazard 2. Shock Hazard Two basic rules must be followed when working near an electrical circuit.

They are, 1. Always turn off power before working on a circuit. 2. Confirm that the circuit is de-energized by checking that it is off using a voltage tester. There are several ways to make sure that a circuit is in de-energized state.

A good practice to see whether a circuit is in off state or not is to connect a lamp across it and see if it lits up or not. If the circuit is equipped with fuses then removing a particular fuse will make sure that specific portion of a circuit is removed from the system. If circuit breaker is used, switching it off will do the same job. Another way to make sure that circuit is absolutely dead is as follows.

A portion of the circuit is connected to ground. So a huge current flow through the conductor making nearby fuse to be melt down. As a result circuit is isolated.

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5. Illumination and lightning

Radiant efficiency =body by the radiatedenergy Total

light of form in the radiatedEnergy

Figure 6 5.1 Some definitions

Light: It may be defined as that radiant energy which produces a sensation of vision upon the human eye. Luminous flux: It is defined as the light energy radiated per second from a luminous body.

Figure 7

Luminous intensity: If dF is the luminous flux crossing any section of narrow cone of solid angle d steradian then, luminous intensity is,

ddFI

Lumen: It is the unit of flux and is defined as the luminous flux per unit solid angle from a source of 1 candle power.

Illuminance or illumination or degree of illumination: Illumination can be defined as the luminous flux received per unit area.

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Illumination = dAdF

Brightness: In the figure let the luminous intensity in the direction OP be 1 lumen per steradian on an area A, the projected area will then be Acos .

Brightness B=cos

1A

Figure 8

5.2 Law of illumination

The illumination of a surface is inversely proportional to the square of the distance of the surface from the source of light. It is true only if the source is a point source.

5.3 Lamberts cosine law

According to this law the illumination of surface at any point is dependent upon the cosine of the angle between the line of flux and the normal at that point.

In the figure,

Intensity of illumination =ABCD AreaF

= cosabcd Area

F

Figure 9

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5.4 Design of lighting scheme Space-height ratio: It can be defined as, The horizontal distance between lamps/Mounting height of lamps This ration stays within the range of 1 to 2. Utilization factor: It is, Total lumens utilized on working planes/Total lumens radiated by lamp. The value of this co-efficient depends on the following factors: The area to be illuminated. Height of the lamps. The color of the surrounding walls. Type of lighting- direct or indirect. Depreciation factor: It is, Illumination under normal working conditions/Illumination when everything is clean. Its value is normally 0.8. Its reverse definition is also true.

5.5 Lighting Schemes Direct lighting Indirect lighting Semi-direct lighting Semi-indirect lighting Type R and PAR type bulbs

5.6 Outdoor lighting for general illumination Outdoor lighting is necessary for security purposes. Two types will be discussed here. Motion detector control Automatic timer control

Figure 10

Motion Detector Control: Motion sensors automatically turn outdoor lights on when motion is detected and turn off a short while after. They are very useful for outdoor security and utility lighting. These lights are needed only when it is dark and people are present, the best way to control might be a combination of motion sensor and photosensor. Incandescent flood lights with a photosensor and motion sensor may actually use less energy than pole-mounted high intensity discharge or low pressure sodium security lights

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controlled by a photosensor. Automatic Timer Control: Timers can be used to turn on and off outdoor lights at specific times. Simple timers are not often used alone for outdoor lighting because the timer may have to be reset often with seasonal variation in the length of night. However, they can be used effectively in combinations with other controls.

Figure 11 5.7 Method of lighting calculation

Watts per square meter method

Lumens or light flux method

ofeachlampefficiencyampswattageofloflampsnoonfactordepreciati

tiontofutilizacoefficien .

or Confinement of utilizationmaintenance factorno. of lampswattage of lamps

efficiency of each lamp

Point to point or inverse square law method

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Figure 12

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Revised by Shama Naz Islam, Lecturer, EEE, BUET

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EEE 314 Lecture 2 Prepared by: Md. Itrat Bin Shams (Sanin)

Contents 1 Basic electrical appliances 2 1.1 Incandescent light bulb . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Fluorescent lamp . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Refrigerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.5 Oven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.6 Microwave Oven . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Fittings and Fixtures 3 2.1 Consumer unit . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Distribution Board . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Service Entrance Panel Design . . . . . . . . . . . . . . . . . . 4 2.4 Types of Branch Circuits . . . . . . . . . . . . . . . . . . . . . 4 2.5 Conduits and Boxes . . . . . . . . . . . . . . . . . . . . . . . . 5 2.6 Electrical Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.6.1 General purpose metal boxes . . . . . . . . . . . . . . . 6 2.7 Installing boxes and cables . . . . . . . . . . . . . . . . . . . . 7 2.7.1 Consideration before wiring, Design factors . . . . . . . 7 2.7.2 Requirement for installing boxes and cables . . . . . . 7 2.7.3 Installing type NM cable in metal boxes . . . . . . . . 8 2.7.4 Making wire connection . . . . . . . . . . . . . . . . . 9 2.7.5 Splicing wire . . . . . . . . . . . . . . . . . . . . . . . . 9 2.7.6 Rain tight boxes and covers . . . . . . . . . . . . . . . 9 2.7.7 Watertight boxes and box extensions . . . . . . . . . . 10 2.8 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.8.1 Special types of switches . . . . . . . . . . . . . . . . . 11 2.8.2 The pull chain switches . . . . . . . . . . . . . . . . . . 11 2.8.3 Single pole switch loop . . . . . . . . . . . . . . . . . . 12 2.8.4 three way switch . . . . . . . . . . . . . . . . . . . . . 12 2.8.5 Four way switch . . . . . . . . . . . . . . . . . . . . . . 13 2.9 Lighting fixtures . . . . . . . . . . . . . . . . . . . . . . . . . 13 3 Earthing 14 3.1 Some definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1.1 Earth electrode . . . . . . . . . . . . . . . . . . . . . . 14 3.1.2 Earthing lead or main earthing conductor . . . . . . . 15 3.1.3 Sub-main earthing conductor . . . . . . . . . . . . . . 15 3.1.4 Earthing continuity conductor . . . . . . . . . . . . . . 15 3.2 Factors on which earth resistance depends . . . . . . . . . . . 15 3.3 Methods of earthing . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.1 Earthging through a water main . . . . . . . . . . . . . 15 3.3.2 Pipe earthing . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.3 Plate earthing . . . . . . . . . . . . . . . . . . . . . . . 15

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1 Basic electrical appliances

1.1 Incandescent light bulb The incandescent light bulb or incandescent lamp is a source of artificial light that works by incandescence. An electrical current passes through a thin filament, heating it and causing it to become excited, releasing thermally equilibrated photons in the process. The enclosing glass bulb prevents the oxygen in air from reaching the hot filament, which would be otherwise rapidly destroyed by oxidation. A benefit of the incandescent bulb is that they can be produced for a wide range of voltages, from a few volts to several hundred volts. Because of their relatively poor luminous efficacy, incandescent light bulbs are gradually being replaced in many applications by fluorescent lights, high-intensity discharge lamps, LEDs, and other devices. 1.2 Fluorescent lamp A fluorescent lamp is a gas-discharge lamp that uses electricity to excite mercury vapor in argon or neon gas, resulting in a plasma that produces short-wave ultraviolet light. This light then causes a phosphor to fluoresce, producing visible light. Unlike incandescent lamps, fluorescent lamps always require a ballast to regulate the flow of power through the lamp.

Figure 1

Figure 2

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1.3 Refrigerator A refrigerator (often called a fridge for short) is a cooling appliance for the storage and preservation of perishable food; food kept in a refrigerator lasts longer than that left at room temperature as the cold inhibits bacterial growth. 1.4 Iron Ironing works by loosening the bonds between the long-chain polymer molecules in the fibres of the material. While the molecules are hot, the fibres are straightened by the weight of the iron, and they hold their new shape as they cool. 1.5 Oven An oven is an enclosed compartment for heating, baking or drying. It is most commonly used in cooking and pottery. Two common kinds of modern ovens are gas ovens and electric ovens. Ovens used in pottery are also known as kilns. An oven used for heating or for industrial processes is called furnace.

1.6 Microwave Oven A microwave oven, or microwave, is a kitchen appliance employing microwave radiation primarily to cook or heat food.

2 Fittings and Fixtures To accommodate a house with electrical appliances, it is necessary to provide adequate fittings and fixture installations. 2.1 Consumer unit A consumer unit is a combination of single row fuses and breakers. If only fuses exist , then it is called fuse box. 2.2 Distribution Board Distribution board is a collection of fuses and breakers. They are placed in a double array. Distribution board is responsible for all the power supply at home.

Figure 4

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2.3 Service Entrance Panel Design Most service entrance panels are provided with main disconnect circuit breaker. It prevents the home from accidents and ensures overcurrent protection. Normally main circuit breaker is connected to two parallel bus bars. Branch circuit breakers are then connected to each of them to feed each of the branch circuits. Branch circuits can also be connected remotely from the service entrance. Branch circuits are responsible to loads to energy sources. They provide wiring between final protecting device and the outlet of a circuit. Each branch circuit has three wires. One is main energy carrier, second one is neutral wire and final one is ground wire. If we need more than rated voltage two branch circuits are to be considered simultaneously. 2.4 Types of Branch Circuits There are mainly two types of branch circuits available. 1. Single outlet branch circuit: Following outlets are connected to a single outlet branch circuit. a. Dishwasher b. Range c. Clothes dryer d. Garbage disposal e. Water heater f. Each appliances rated more than 1000W g. Each permanently connected motor rated half horse power or more. 2. Two or more outlet branch circuits: Different wires are used for different branch circuits, such as,

Circuit Rating in AMPs

Copper Wire Size

15 14 20 12 30 10 40 8 50 6

15 amps branch circuit is normally used for ordinary lighting instruments. 20 amps circuits are used for refrigeration purpose, pantry, breakfast room, dining room etc. When 20 amps circuits are provided both 15 and 20 amps receptacles are to be provided. A 15 amps circuit can be fed into a 20 amps receptacle but reverse cannot be done. 30 or 40 amps branch circuits are used for clothes dryer and other high current equipments in dwelling places.

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2.5 Conduits and Boxes

Types of conduits used: Rigid steel: This type of metal conduit is supplied in 10 foot lengths of steel or aluminium. It can be of 6 inches of diameter. Its inner surface is smooth. If this conduit has any chance to come in contact with the earth then a protective coating is necessary. For cinder filled environment plastic coating can be given. Inter mediate metallic (IMC): Diameter of IMC can be up to 4 inches and it has thinner wall than rigid type. Electrical metallic tubing (EMT): Electrical metallic tubing is similar to Rigid type but it is thinner and its diameter can be up to 4 inches. It is not threaded and has its own type of connectors. Flexible steel conduit: It is flexible in nature and can be given any shape. When used a separate grounding wire must be provided as it has much higher resistance.

Rigid non-metallic conduit and Electrical non-metallic tubing (ENT): Non metallic conduits are made of Polyvinyl Chloride (PVC), fiberglass, polyethylene, transite and others. There are two basic types: rigid metal type and electrical non-metallic tubing. It can be bent and given any shape via hot air, hot liquid or hot box. No flames should be used. When two parts are needed to be joined a solvent-type cement.

2.6 Electrical Boxes

Electrical boxes can best described as the termination enclosures that accommodate the entrance of the various types of conduits, armored cables or non-metallic sheathed cables for the purposes of splicing the wires and providing circuit outlets for switches, receptacles, fixtures and other electrical accessories. Selection of boxes are dependent on the following things: The number of wires entering The kind and number of devices attached to it The wiring method used

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2.6.1 General purpose metal boxes General purpose boxes are of three types: Switch boxes: Switch boxes are gangable. This means two or three boxes can be connected together. Octagon Boxes: These types of boxes are used for special purposes. Square boxes: Steel square boxes are versatile in nature as they can be used for both concealed wiring work or exposed wiring installations. Ceiling pan boxes: These are used in roof tops.

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2.7 Installing boxes and cables

2.7.1 Consideration before wiring, Design factors An electric service with adequate capacity Wires of sufficient capacity throughout A sufficient number of circuits A sufficient number of plug in receptacles An adequate number of lights Wall switches in sufficient number Provision for security for both inside and outside 2.7.2 Requirement for installing boxes and cables In walls: Base receptacle boxes are normally placed 12 or 16 inches high above the ground. Wall switch boxes are normally located 44-48 inches above the floor on the latch side of each door. In ceiling: Proper placement must be made so that no harm is done on the roof.

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Under floors: Similar remedies are taken.

2.7.3 Installing type NM cable in metal boxes Wires must be placed so that proper connection is possible.

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2.7.4 Making wire connection Striping NM cable sheaths: For this a stripper is used. NM cable is penetrated to the stripper, and it is squeezed and moved to cut adequate amount of insulation. A knife is used to remove the sheath. Stripping armored cable sheaths: A fine tool hacksaw is the best for this job. Stripping wire insulation: To strip wire insulation one must not cut the sheath at right angles, he should use 60 degree angle. This prevents unnecessary wire cutting.

2.7.5 Splicing wire Proper splicing is necessary to avoid accidents in case of heavy loads. Wirenut Connectors: This is the most basic type of connection between two wires. Electrical tape can be wrapped around the base of the wirenut and the wires. Crimp Connectors: Crimp connectors are used when cables entering metal boxes require the splicing individual bare grounding wires together. Here wires are twisted together first and then a ring is used to make the contact. Ring is squeezed to make connection. Connectors for Larger wire sizes: For this clamp or split bolt type connectors are used. 2.7.6 Rain tight boxes and covers They are usually made of painted sheet metal and have a guard to protect against the entry of rain falling on top of the box. Some feature like self-closing is also available.

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2.7.7 Watertight boxes and box extensions These are built to protect switches from temporary immersion or sprinkling. Box extensions are available for this sort of fittings. They eliminate costly and time consuming breaking and repairing of walls.

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2.8 Switches 2.8.1 Special types of switches Mercury switches: Uses mercury for a contact so the switch must be installed right side up and vertical for smooth operation. Dimmer switches: They are used to control the intensity of light and conserve energy. Time delay switch: To make a light automatically turned off after someone left that place. Pilot light witch: Useful for controlling outdoor or remote lights. Lighted handle switch: Helps to find a switch in the dark. Manual timer switch: Has a spring wound timer that can be used up to 12 hours. Clock switch: Has a digital read out of the time built into switch. Locking switch: Can be wired into circuits supplying outlets. 2.8.2 The pull chain switches This is one of the least expensive ways to build a switch.

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2.8.3 Single pole switch loop When this type of switches are used two wires are necessary. Black wire connects with the power line and white wire with the shell of the lighting fixture. A switch must be installed in a hot wire and not in a neutral wire. It makes the device connected to the switch to be in ground potential. This prevents any shock from the device. 2.8.4 Three way switch This type of switch is used for a hall light that can be controlled from the bottom and top of a staircase or an outside light be controlled from inside and outside of a house. A three way switch is a single pole double throw switch. Three way switch means it has three terminals and not three switches.

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2.8.5 Four way switch It is used to control a light from three different points. Here a three way switch is installed near the load and another distant from the load. The four way switches can be installed between the three way switches.

2.9 Lighting fixtures There various types of lighting fixtures. Some are, Emergency light Flood light Safelight Safety lamp Searchlight

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Security lighting Street light Spotlight Torch lamp or torchiere Landscape or outdoor lighting Night light

Figure 22: Four way switch

3. Earthing

3.1 Some definitions 3.1.1 Earth electrode The conductor embedded in the ground for the purpose of making connection with the general mass of earth is known as earth electrode and the wire which connects overhead. There are three types of artificial electrodes: Driven electrodes: The electrode is made of metal rod or pipe having a clean surface line. Rod electrodes of steel or iron should have diameter of 16mm and those of copper at least 12.5mm. Strip electrodes: These are made of copper strips of area 25mmX1.6mm in cross section. They are buried under the ground not less than 2.5m. Plate electrodes: A plate of copper or galvanized iron of 0.6X0.6X0.006m for iron and 0.6X0.6X0.003m for copper is buried with the face vertical in an alternate layer of coke and salt.

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3.1.2 Earthing lead or main earthing conductor The main wire that connects the earth electrode with main circuit board or the earth wire running through distribution, transmission lines is known as earthing lead. 3.1.3 Sub-main earthing conductor The earth wire that runs between the main switch board to the distribution board. 3.1.4 Earthing continuity conductor The wire running between the distribution board to the various plugs and appliances. 3.2 Factors on which earth resistance depends a. Materials of electrodes and earth wire. b. Size of electrode and earth wire. c. Temperature of the soil. d. Moister of the soil. e. Depth to which it is embedded. f. Quantity of coal and charcoal in the earth electrode pit. Maximum value at the earthing side should be 5 ohms. But for substations it should be of 0.5 to 1.00 ohms. 3.3 Methods of earthing 3.3.1 Earthging through a water main Here a water main is used as earth electrode.

3.3.2 Pipe earthing If water main is not available then a galvanized pipe can be used. Its length should be 2.75m for wet soil and 2.75m for dry soil. Alternate layers of coke and salt is used around the earth electrode for best result. In summer season it may be necessary to pour buckets of water to decrease the resistance value. 3.3.3 Plate earthing Here, earthing connection is provided via copper plate of size 60cmX60cmX6.35mm or G.I. pipe of size 60cmX60cmX3.18mm. Use of copper plate is limited nowadays.

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EEE 314 Lecture 3 Prepared by: Md. Itrat Bin Shams (Sanin)

Contents 1 Safety Rules 2 1.1 Laboratory safety . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.1 Safety of person . . . . . . . . . . . . . . . . . . . . . . 2 1.1.2 Safety of equipments . . . . . . . . . . . . . . . . . . . 2 1.2 Additional items related to personal and equipment safety 3 2 Sub-Stations 4 2.1 Classification of sub-stations . . . . . . . . . . . . . . . . . . . 4 2.1.1 In accordance with the service . . . . . . . . . . . . . . 4 2.1.2 In accordance with the service voltage . . . . . . . . . 4 2.1.3 In accordance with mounting . . . . . . . . . . . . . . 4 2.2 Essential parts of a sub-station . . . . . . . . . . . . . . . . . 5 2.2.1 Transformer . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2 Insulators . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.3 Conductors . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.4 Isolators . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.5 circuit breakers . . . . . . . . . . . . . . . . . . . . . . 7 2.2.6 Load interrupt switches . . . . . . . . . . . . . . . . . 7 2.2.7 Power transformers . . . . . . . . . . . . . . . . . . . . 8 2.2.8 Current transformers . . . . . . . . . . . . . . . . . . . 8 2.2.9 Potential transformer . . . . . . . . . . . . . . . . . . . 8 2.2.10 Carrier current equipment . . . . . . . . . . . . . . . . 8 2.2.11 Control cables . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.12 Air break and disconnect switch . . . . . . . . . . . . . 8 2.2.13 Switch board . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.14 Control room . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 Advantage and disadvantage of outdoor substation as compared to indoor substation . . . . . . . . . . . . . . . . . . . . 9 2.4 Design of a substation . . . . . . . . . . . . . . . . . . . . . . 9 2.5 Layout of substations . . . . . . . . . . . . . . . . . . . . . . . 10 2.5.1 Single Busbar . . . . . . . . . . . . . . . . . . . . . . . 10 2.5.2 Mesh Substation . . . . . . . . . . . . . . . . . . . . . 11 2.5.3 One and a half Circuit Breaker layout . . . . . . . . . 11 2.6 BBT (Bus Bar Trunking) . . . . . . . . . . . . . . . . . . . . . 12 2.6.1 Protection of BBT . . . . . . . . . . . . . . . . . . . . 12

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1 Safety Rules

1.1 Laboratory safety While working in a laboratory, safety of a person and equipment is necessary. These are discussed separately. 1.1.1 Safety of person The flow of electricity can adversely effect anyones body in at least three ways. It causes muscle spasms and paralysis. It can electrolyte blood in body and make bubbles. It also can burn skin. Only 50mA current is enough for paralysis of heart. What can be done if anyone is shocked: 1. The cause of shock must be removed first. it is necessary to use nonconducting materials such as woods or plastic to remove live wires or substances from ones touch. 2. If the person shocked is not breathing, artificial respiration should be given to him. 3. If the victim is conscious, he should be in comfortable situation and taken to a doctor. Precautions to prevent shocking: 1. One should avoid become a victim. Voltages should not be allowed to come in contact with the body. 2. No bare conductors should be touched without knowing what it really stands for. How can a person get shocked: 1. Any person needs only one conductor and a ground to get shocked. This means if anyone touches a live wire a circuit is formed through his body. Current can easily pass through him. 2. There are a lot of capacitors in a house. These instruments can hold charges for a long time. If anyone touches them he can get a surprise shock. Skin posses a small resistance value. When a dry skin comes across a contact, shock may be mild. But a sweaty skin can produce a larger shock. A fat persons probability to get shock is more than a light person as thin body has high resistance. There are some non-electrical hazards around electrical and electronic equipments. Like some batteries can discharge chemical materials that is harmful for health. These batteries can produce explosive hydrogen gases. Cathode-ray tubes are used in some electrical appliances. These tubes have high pressure inside them. Pressure is around 15 pounds per square inch. If it explodes due to some mis-operation, then it is possible that broken glasses from tube will move with high velocity and injure people. 1.1.2 Safety of equipments About all general electrical instruments work with constant voltage. So amount of current passing through them depends on load resistive value. If it is small current is large and if it is large current is small. Power consumed by any equipment thus depends on current. Things are damaged if too much current passes through them. Fuses and circuit breakers are provided to protect a system. But they are usually provided to

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protect transmission lines. Fuses and circuit breakers operate within fraction of a second. A lot of damages can be done within this time to electrical equipments. Some ways to avoid common types of troubles are: 1. Rated wires should be used so that it can carry right amount of current of necessary. Resistor values should be maintained to that value where safe operation os possible. 2. Indicating and metering instruments should be handled according to usual procedure. Such as a voltmeter has a high resistance and a small current will flow through it. So voltmeters should be connected in parallel to others. 3. Ammeters must be connected in series in any circuit. As they have low resistance. To distinguish the connection between voltmeter and ammeter, we can use the word voltage across and current through. Ammeters can be kept in safe by using ammeter shunt switches. If a huge current tend to flow through the ammeter shunt switch will be off and ammeter will be safe. 1.2 Additional items related to personal and equipment safety Meters should be kept in their highest position before energizing a circuit. It is important that meters be hooked up with correct polarity. Resistors should have power ratings at least two times greater than expected power dissipation. If it is necessary to change a certain portion of a circuit, it is recommended that all the parts be energized. In all cases voltage sources should not be applies to desired point suddenly. It should be brought up from zero value to highest value slowly. There should be a first aid kid box for every lab in case of minor cuts and burns. If fuses are blown out, correct rated fuses must be replaced in place of older one. All labs should have decade resistance boxes and resistor substitution boxes. Decade resistor boxes are provided to make estimation of unknown resistor values. Resistor substitution boxes are used in hooks up where resistances are altered. Ohmmeters should be turned off after use. This will make sure of linger battery life. Any malfunctioing instrument should not be repaired by untrained personnel. Fire hazards or burns can result from poor soldering equipments. Poor insulation can make high current to flow as well as starting fire. Resistors and other equipments should not be altered if circuit is energized. Burnt out florescent bulbs should be replaced carefully as there is a chemical coating inside the bulb. Prevent dangerously high voltage, reverse winding connection of transformers must not made. Commercial transformers should be properly ventilated. Neutralization of any acid or battery electrolyte that may get on clothing must be made. When acid and water is mixed, acid must be poured in water.

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2 Sub-Stations

A sub-station can be defined as combination of apparatus that transforms the characteristics of electrical energy from one form to other form. For example, from alternating to DC or from one level of voltage to other. 2.1 Classification of sub-stations Sub-stations can be classified on the basis of some features. They are: 2.1.1 In accordance with the service Static: The instruments used to change electrical energy characteristics are static. So it changes voltage of an a.c signal. Converting: In this type A.C. energy is changed to D.C. energy. 2.1.2 In accordance with the service voltage Extra high voltage: Here voltage level is changed in the range of 66kV in order to transmit energy. It is also called transmission sub-station. Distribution Sub-station: In this sub-station voltage is stepped down to 400 volts. Industrial sub-station: Different industries need different voltage levels to make their machines work. Industries take power from 11kV or 66kV feeder line and then convert the voltage level according to their need via industrial substation. Substation for power factor correction: Due to the presence of inductance power factor falls at the end of the transmission line. In order to improve power factor, synchronous condensers are used. Such installations are known as power factor correction sub-station. Frequency changing sub-stations: These sub-stations are used to change frequency of one signal to another value. 2.1.3 In accordance with mounting Indoor type substation: These sub-stations are used with open and enclosed chambers or compartments. The chamber space in which one main bus bar connection is mounted is called cell, cubicle or compartment. These sub-stations are built to handle voltage up to 11000 volts but can also be used to operate in 33000 or 66000 volts. Surrounding air in this type of installation is filled with dust, gases and fumes. According to construction indoor type substations can be further divided into: Sub-stations with integrally built type: Here apparatus are installed in site. Cell structure is constructed with concrete or brick. Sub-stations with composite built type: A switchgear room is provided for control. Compartments of these sub-stations are taken from metal cabinets or enclosures, each of which contains the equipment of one main connection cell. Unit type factory fabricated sub-stations: It is fully preassembled. After installation only incoming and outgoing connections are to be provided.

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Outdoor type sub-stations: These are of two types. Pole mounted substation: These are installed on certain poles. They are of H-pole and 4-pole. They carry transformers of capacity up to 200kVA. These types of sub-stations are cheap, simple and smaller. Foundation mounted sub-station: These sub-stations are used to handle primary and secondary transmission. As they carry huge machineries so it is necessary to place them in such a site where there is sufficient access of heavy transport.

2.2 Essential parts of a sub-station 2.2.1 Transformer Transformers are mainly used in voltage conversion purposes. A transformer has primary and secondary coils and they are insulated from each other by insulation. There is a steel core which is made of laminations. Transformers are placed in a container and transformer oil is placed between the container and transformer to make sure of insulation. Transformers are divided according to two categories. In accordance with the type of core: It is again divided into two parts. Core type transformer: Here low voltage winding is provided near the core. It is because low insulation is needed for low voltage side.

Shell type transformer: Here shell type core is provided.

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In accordance with the type of cooling: Here transformers are again subdivided in following categories. Oil filled self cooled: Here a type of insulating oil is provided for cooling purposes. Oil provided must be of high quality and it should be replaced after specific periods of time. Oil-filled water cooled: Here oil that is used for cooling purpose is cooled by water coils circulating inside the container. Here convection method of heat transfer is used. Air blast type: It is used for transformers of capacity 33kV or above. Strong air is directed towards the transformer coil through ducts. 2.2.2 Insulators The porcelain insulators used in sub-station are of post and bushing type. They serve as both support and insulation purpose. Post type: A post insulator consists of porcelain body, cast iron cap and flanged cast iron body. Bus bars are bolted to the cap either directly or fixed by means of a bus bar clamp.

Figure 3: Post type insulator

Bushing type: It consists of porcelain shell body, upper and lower locating washers and mounting flange. They are designed to handle currents above 2000A.

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2.2.3 Conductors The substation buses can be of the following types: a. Rigid buses of solid conductor or tubing. b. Strain bus of cables. An ideal conductor should fulfill the following requirements:

a) Should be capable of carrying the specified load currents and short time currents b) Should be able to withstand forces on it due to its situation. These forces

comprise self weight and weight of other conductors and equipment, short circuit forces and atmospheric forces.

c) Should be corona free at rated voltage. d) Should have the minimum number of joints. e) Should need the minimum number of supporting insulators. f) Should be economical

Nowadays aluminium is used over copper wires. It is because aluminium has higher conductivity, lower cost for equal current carrying capacity, excellent corrosion resistance and ease of formability. 2.2.4 Isolators Isolators are used to isolate a certain portion of a system after switching of circuit breakers. Sometimes isolators are used to operate as a circuit breakers but their operation as this is strictly limited due to certain conditions. Isolators are of two types, Single pole isolators. Three pole isolators. Isolator design is considered in the following aspects:

1) Space Factor 2) Insulation Security 3) Standardization 4) Ease of Maintenance 5) Cost

2.2.5 circuit breakers Circuit breakers are intended to perform the following tasks: 1. To carry the full load current continuously. 2. To open and close the circuit on no load. 3. To make and break the normal operating current. 4. To make and break the short circuit current of magnitude up to which it is designed for. 2.2.6 Load interrupt switches They are used to open and close high voltage circuits. They should be handled carefully.

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2.2.7 Power transformers Power transformers are used to step up voltage at generation end for transmission purpose and step down voltage for farther distribution of power. Different types of transformers such as, naturally cooled, oil immersed, two winding three phase transformers, air blast cooled transformers are used. Power transformers are usually the largest single item in a substation. Because of the large quantity of oil, it is essential to take protection against the spread of fire. Hence, the transformer is usually located around a sump used to collect the excess oil. 2.2.8 Current transformers Current transformers are used in indicating and metering instruments. They are used in ammeters, wattmeter, watt-hour meter etc. Primary coils of these transformers are placed in the circuit where current is ti be measured. Secondary coil takes current reading in a suitable value so that indicating instrument can show the reading. 2.2.9 Potential transformer Potential transformers are also used in metering and indicating instruments such as voltmeter, wattmeter, watt-hour meter. Primary coil is directly connected to busbars where voltage is to be measured. Secondary coil converts the voltage reading to a suitable value so that indicating instrument can show this in full scale. 2.2.10 Carrier current equipment These are used for communication, relaying, telemetering and supervisory control. 2.2.11 Control cables To carry different voltage levels, different cables (say 10 or 37 or 61 conductor grouped cables) are used. It is necessary to control these cables inside a conduit. For this, control cables are provided. Ducts are used to run from switch gear rooms to the beginning and end of a conduit. 2.2.12 Air break and disconnect switch For lines with 46kV or lower voltages, disconnect switches are provided with single pole construction and hook stick operated mechanism. For 110kV or upper voltage systems group operated mechanism is provided where all the six poles are operated with one handle. 2.2.13 Switch board Switch boards are consisted with meters, relays and control equipments. The essential meters are placed at the bottom. Control equipment half way through, so as to facilitate operation. It is shown in following figure.

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2.2.14 Control room A control room is provided to monitor all the readings and to have an excess to all connection points. Normally an operator is given for each control room.

2.3 Advantage and disadvantage of outdoor substation as

compared to indoor substation The outdoor substation has following advantages: The construction work needed is much smaller than the indoor substation. Installation cost of switchgear is low. Adequate space between two adjoining equipment can be provided. Erection is made in less time. Whole structure is properly viewed, so that fault can be easily located. The scheme extension is easier. Disadvantages of outdoor substations are, Dust and dirt use to formulate on contact switches. This makes maintenance cost higher. In rainy or snow falling seasons switching becomes complicated. The installation suffers from security as unauthorized persons can easily penetrate the structure.

2.4 Design of a substation Following steps should be followed in designing a substation: 1. Make a single line diagram of the total system showing all the connection between bus bars, circuit breakers and reactors. 2. Design the layout of the switchgear depending on the size, capacity of the substation. 3. Circuits should be designed in such a way that minimum amount of risk will occur in case of its failure. 4. The layout should be such that any faulty section can be isolated without effecting the other portions. 5. There should be provision for easy and safe excess for maintenance and repairing purpose.

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6. Partitions should be provided in order to differentiate one part from other. 7. Reactors must be of rating that can limit the short circuit current. This makes capacity of the circuit breaker adequate. 8. To avoid using huge circuit breakers the current per circuit breaker should be limited to 2000A. 9. Fire extinguishing system must be provided. 10. The earth conductor should have sufficient capability to carry any amount of fault current. 11. Automatic electric gear should be given. 12. Power cables should be separated from control cables. 13. In order to avoid fire hazard, fire proof control room and switch room have to be provided. 14. Arrangement for oil handling must be safe.

2.5 Layout of substations There can be different layouts of a substation. Three are given below: 2.5.1 Single Busbar Layout is given in figure 6. Operation is very simple in this layout design. But its reliability is very low as if bus goes out of service all the loads will be disconnected from power supply. There is a provision to support cheap future connection of feeders. Some features of this scheme are, Each circuit is protected by its own circuit breaker and hence plant outage does not necessarily result in loss of supply. A fault on the feeder or transformer circuit breaker causes loss of the transformer and feeder circuit, one of which may be restored after isolating the faulty circuit breaker. A fault on the bus section circuit breaker causes complete shutdown of the substation. All circuits may be restored after isolating the faulty circuit breaker. Maintenance of a feeder or transformer circuit breaker involves loss of the circuit. Introduction of bypass isolators between busbar and circuit isolator allows circuit breaker maintenance facilities without loss of that circuit.

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2.5.2 Mesh Substation Layout of this scheme is given in figure 7. Some characteristics are, Operation of two circuit breakers is required to open or close a circuit. Circuit breakers may be maintained without loss of supply or protection, and no additional bypass facilities are required. Breaker faults will involve the loss of a maximum of two circuits.

2.5.3 One and a half Circuit Breaker layout The reason that such a layout is known as a 1 and 1/2 circuit breaker is due to the fact that in the design, there are 9 circuit breakers to protect the 6 feeders. Thus, 1 and circuit breakers protect 1 feeder. Some characteristics of this design are: Here arrangement is complex and it is also expensive. There is provision to operate one circuit or group of circuits. reliability is very high in case of loss of power.

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2.6 BBT (Bus Bar Trunking)

Bus bar trunking is used to increase the current carrying capability of a system. Here multiple buses are used in parallel.

This Unified Recommendation is for the test and installation of busbar trunking systems arranged outside of switchboards for supplying section or distribution boards or consumers, instead of cables. They are not recommended to be installed in hazardous areas or on the exposed weather deck. 2.6.1 Protection of BBT General Systems should comply with the specific requirements of local electrical codes. Temperatures should be in the range from 0 to 45oC. Nearby foreign bodies or water pipes must be placed away from bus bars to protect them. The system should be designed to withstand a vibration level of 1mm amplitude in the frequency range of 2 Hz to 13.2 Hz and of 0.7g acceleration in the frequency range of 13.2 Hz to 100 Hz. It should be suitable for automatic draining where condensation is possible. Fire test arrangements should be compatible with the local codes.

Revised by Shama Naz Islam, Lecturer, EEE, BUET

CONTENTS

EEE 314 Lecture 4

Prepared by: Md. Itrat Bin Shams (Sanin)

Contents

1 Home security and fire alarm system 21.1 Types of sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 The alarm system . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Digital security pad . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Fire alarms for the home . . . . . . . . . . . . . . . . . . . . . 4

1.4.1 Heat detectors . . . . . . . . . . . . . . . . . . . . . . . 51.4.2 Smoke detectors . . . . . . . . . . . . . . . . . . . . . . 6

2 Television connection 62.1 Typical problems with antenna . . . . . . . . . . . . . . . . . 6

2.1.1 Congested area problem . . . . . . . . . . . . . . . . . 62.1.2 Fringe area problems . . . . . . . . . . . . . . . . . . . 6

2.2 Cable television wire . . . . . . . . . . . . . . . . . . . . . . . 6

3 Telephone wiring 63.1 Telephone regulation . . . . . . . . . . . . . . . . . . . . . . . 73.2 Number of telephones that can be connected . . . . . . . . . . 83.3 Safety consideration . . . . . . . . . . . . . . . . . . . . . . . . 8

4 Burglar alarm 94.1 Access Control . . . . . . . . . . . . . . . . . . . . . . . . . . 94.2 A simple sound activated burglar alarm system . . . . . . . . 10

5 CCTV 105.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 105.2 THE CAMERA . . . . . . . . . . . . . . . . . . . . . . . . . . 115.3 THE MONITOR . . . . . . . . . . . . . . . . . . . . . . . . . 115.4 SIMPLE CCTV SYSTEMS . . . . . . . . . . . . . . . . . . . 11

6 Sprinkler 126.1 Fire sprinkler . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7 Elevators 15

1

1. Home security and fire alarm system

8 Intercom 168.1 Types of intercoms . . . . . . . . . . . . . . . . . . . . . . . . 16

8.1.1 Two wire . . . . . . . . . . . . . . . . . . . . . . . . . 168.1.2 Four wire . . . . . . . . . . . . . . . . . . . . . . . . . 16

9 Air conditioning 179.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.2 Air conditioning application . . . . . . . . . . . . . . . . . . . 18

9.2.1 Comfort application . . . . . . . . . . . . . . . . . . . 189.2.2 Process application . . . . . . . . . . . . . . . . . . . . 18

9.3 Basic principle of air conditioning . . . . . . . . . . . . . . . . 19

10 Local area network (LAN) 20

11 Home heating system 2111.1 Types of home heating systems . . . . . . . . . . . . . . . . . 21

11.1.1 Traditional Furnaces . . . . . . . . . . . . . . . . . . . 2111.1.2 Electric Heat Pump . . . . . . . . . . . . . . . . . . . . 2111.1.3 Radiant Baseboard Heat . . . . . . . . . . . . . . . . . 2111.1.4 Radiant Ceiling or Floor Heat . . . . . . . . . . . . . . 22

1 Home security and fire alarm system

For home security system following sensors are used.

1.1 Types of sensors

Foil type sensors on windows that works if someone penetrates throughit.

Magnetic or push button switch on a door or window frame. Panic buttons placed at strategic locations that are pushed to activatethe alarm system.

Heat detectors and smoke detectors to protect a house. High temperature heat detector. Various types of detectors for vibration detection, infrared or ultrasonicmotion detector, low temperature detector to indicate a home is losingheat, pressure sensing detector under a carpet or floor.

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1.2 The alarm system

1.2 The alarm system

There is a central alarm center that is used to monitor all the alarms in ahome. Sometimes there is a automatic telephone dialer in a home, that isused to call the police in case of unknown intruder. the around-the-clockservice can be used which indicates what type of alarm is being initiated.All these are controlled by central alarm system.

There are two basic circuits used for sensing purposes. They are normallyclosed and normally open.

1. Normally Closed (NC): Normally closed circuits are closed when inactive mode. If somehow it is opened then alarm is initiated. A goodexample of it is sensors used in windows and doors. Here if the widowor door is closed the two contact path in the circuit are intact. But ifsomeone opens it contact is broken, as a result alarm is triggered.

2. Normally Open (NO): Normally open circuits are opened while in activemode. If it is closed then alarm is initiated. It is used in pressuresensing for example. When someone sits on a sofa two contact pathesin the sensing circuit are closed. As a result alarm is On.

Another type of sensing available is delayed sensing. It is used to initiatealarm after a certain time of sensing circuit operation. It is used in fire alarmsystem where there is a time delay before the doors are closed in a space.

1.3 Digital security pad

In fig. 1 a typical digital security pad is shown. It allows some time to makean alarm system armed so that the user can safely leave the place coveredby the system without initiating the alarm.

There are three lights. Red light blinking means activity is reported andit will continue to do so until someone clears the system. Green light blinkswhen a sensor goes to an abnormal position, such as a windows opening.Yellow light is lit if one or more sensors are shunted out.

To remove the shunt, the sensors should first be removed to normal posi-tion and the secret code be entered. The green light will be out and red andyellow light will be in steady position. If the secret code is entered again,

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1.4 Fire alarms for the home

Figure 1: Digital security pad

red and yellow light will be out and green light will glow to indicate normalposition of sensors. In case of shunted sensors, full system may not returnedto its normal position. For this red light will go out when secret code isentered, but green light will blink to show shunted out sensors. A blinkinggreen light always indicates an abnormal condition and the number of blinksindicate what type of condition it is.

1.4 Fire alarms for the home

This alarm system can be of stand alone type or conjuncted with centralalarm system. The stand alone type can be a smoke detector but not aheat detector. There are two types of detector: one that detects amountof radioactive material called ionization type, and another is optical sensingtype.

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1.4 Fire alarms for the home

1.4.1 Heat detectors

Heat detector has a vital limitation. In most of the cases heat detectors areactivated after smoke, fire hazard reaches above tolerance limit.

Figure 2: Flush mounting

Figure 3: Wiring in a heat detector

A typical flush mounting heat detector is shown in fig. 2. Wiring con-nection of a heat detector is shown in 3. There is a plasticizing material. Ifsomehow it penetrates beyond the terminal screws into the interior of theunit or beyond the plastic discs into the raised vent opening, the calibrationof the rate of rise feature will be altered, usually resulting in a false alarm.

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2. Television connection

1.4.2 Smoke detectors

Smoke detectors detect any presence of smoke in a room. There are basicallytwo types of smoke detectors.

1. Ionization detector: When the detector is connected to power source aradioactive material can ionize the air between two electrodes.

2. Photoelectric detector: There is a light source and a photocell. Innormal condition no light falls on the photocell. When smoke particlesenter the chamber, it causes light to reflect on the photocell.

2 Television connection

2.1 Typical problems with antenna

2.1.1 Congested area problem

If high congestion of signals exist in a area, it is possible to achieve betterresult by having co-axial lead in cables.

2.1.2 Fringe area problems

Fringe area problem exist if strength of the signal arriving from the trans-mitter is weak. It can have noises, interferences, flutter and ghosts. It canbe reduced by using reflectors and director elements or antenna boosters.Also higher the receiving antenna is better is the chance to receive the signalcorrectly.

2.2 Cable television wire

For new building construction, the electrical contractor who installs housewiring usually installs the co-axial cable and TV outlets. It is essential thatelectricians be familiar with type RG59/U TV co-axial cable requirement.The co-axial cable must have a type F59 coaxial connector installed on itsend to permit it to be connected for use. In figure one type of connector isshown.

3 Telephone wiring

Making modification to any home telephone system is simple, safe and inex-pensive. So telephone wiring is not that complex.

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3.1 Telephone regulation

Figure 4: Cable prepared for connector

3.1 Telephone regulation

Telephone company will maintain all the responsibility for the wire from theircentral office to the point indicated in the figure. It may also be requiredthat their should be some sort of disconnecting option from the main line tohome. For this purpose existing outlets or modular jack are used. In mostof the cases network interface is used.

Figure 5: Point of demarcation

Telephone company can give a network interface if it is required by thecustomer. It is very convenient way to be connected to the telephone com-panys services. If repair to the line is needed interface can be disjointed and

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3.2 Number of telephones that can be connected

Figure 6: Network interface

all the phones in the home will be disconnected from main line.

3.2 Number of telephones that can be connected

Each phone needs a ringing power known as ringer equivalency number(REN). If number of phones connected in a home has REN summation lessthat 5, there will be no problem. But if it is more than 5 then not all thephones can be connected simultaneously. In this case phones with lower RENvalues have to be used.

3.3 Safety consideration

Though telephone lines usually carry a low current, it is necessary to performsome precautions while working with them.

A telephone must be disconnected before working with it. Thoughtelephones carry a little current, to ring the phone a slightly morecurrent is needed. So anyone may get a surprised shock while thephone rings.

Wires and screws should not be touched.

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4. Burglar alarm

When a thunderstorm or lighting is nearby, no one should work withtelephone lines.

Persons with pacemakers shold not work with telephone lines. Telephones with lighted dials usually draw powers from telephone lines.But some use to do it by a little transformer. It should be disconnectedbefore working.

Telephones are not to be used near water. If walls are to be drilled or cut, cautions must be taken so that nointernal pipes are cut.

There should be no loose wires. They can introduce severe hazards.

4 Burglar alarm

Burglar (or intrusion), fire and safety alarms are found in electronic form to-day. Sensors are connected to a control unit via either a low-voltage hardwireor narrowband RF signal, which in turn connects to a means for announcingthe alarm, hopefully to elicit some response. The most common security sen-sors indicate the opening of a door or window or detect motion via passiveinfrared (PIR). In new contsruction systems are predominately hardwiredfor economy while in retrofits wireless systems may be more economical andcertainly quicker to install. Some systems are dedicated to one mission, oth-ers handle fire, intrusion, and safety alarms simultaneously. Sophisticationranges from small, self-contained noisemakers, to complicated, multi-zoneddigital systems with color-coded computer monitor outputs. Many of theseconcepts also apply to portable alarms for protecting cars, trucks or othervehicles and their contents.

4.1 Access Control

Access Control and Bypass Codes To be useful, an intrusion alarm system isdeactivated or reconfigured when authorized personnel are present. Autho-rization may be indicated in any number of ways, often with keys or codesused at the control panel or a remote panel near an entry. High-securityalarms may require multiple codes, or a fingerprint, badge, hand-geometry,retinal scan, encrypted response generator, or other means that are deemedsufficiently secure for the purpose. Failed authorizations should result in analarm or at least a timed lockout to prevent experimenting with possible

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4.2 A simple sound activated burglar alarm system

codes. Some systems can be configured to permit deactivation of individualsensors or groups. Others can also be programmed to bypass or ignore indi-vidual sensors (once or multiple times) and leave the remainder of the systemarmed. This feature is useful for permitting a single door to be opened andclosed before the alarm is armed, or to permit a person to leave, but notreturn. High-end systems allow multiple access codes, and may even permitthem to be used only once, or on particular days, or only in combination withother users codes (i.e., escorted). In any case, a remote monitoring centershould arrange an oral code to be provided by an authorized person in caseof false alarms, so the monitoring center can be assured that a further alarmresponse is unnecessary. As with access codes, there can also be a hierarchyof oral codes, say, for furnace repair person to enter the kitchen and base-ment sensor areas but not the silver vault in the butlers pantry. There arealso systems that permit a duress code to be entered and silence the localalarm, but still trigger the remote alarm to summon the police to a robbery.

4.2 A simple sound activated burglar alarm system

Figure 7: Simple burglar alarm

5 CCTV

5.1 INTRODUCTION

As the name implies, it is a system in which the circuit is closed and all theelements are directly connected. This is unlike broadcast television whereany receiver that is correctly tuned can pick up the signal from the airwaves.Directly connected in this context includes systems linked by microwave,infrared beams, etc.

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5.2 THE CAMERA

5.2 THE CAMERA

The starting point for any CCTV system must be the camera. The cameracreates the picture that will be transmitted to the control position. Apartfrom special designs CCTV cameras are not fitted with a lens. The lens mustbe provided separately and screwed onto the front of the camera. There is astandard screw thread for CCTV cameras, although there are different typesof lens mounts.

Figure 8:

5.3 THE MONITOR

The picture created by the camera needs to be reproduced at the controlposition. A CCTV monitor is virtually the same as a television receiverexcept that it does not have the tuning circuits.

5.4 SIMPLE CCTV SYSTEMS

The simplest system is a camera connected directly to a monitor by a coaxialcable with the power for the camera being provided from the monitor. Thisis known as a line powered camera.

The next development was to incorporate the outputs from four camerasinto the monitor. These could be set to sequence automatically through thecameras or any camera could be held selectively.

The basic CCTV installation is shown where the camera is mains poweredas is the monitor. A coaxial cable carries the video signal from the camera tothe monitor. Although simple to install it should be born in mind that the

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6. Sprinkler

Figure 9:

Figure 10:

installation must comply with the relevant regulations such as the Instituteof Electrical Engineers latest edition.

6 Sprinkler

6.1 Fire sprinkler

Fire sprinklers are an active fire protection measure subject to stringentbounding. They are connected to a fire suppression system that consists ofoverhead pipes fitted with sprinkler heads throughout the coverage area. Fire

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6.1 Fire sprinkler

Figure 11:

Figure 12:

sprinkler systems for high-rises are usually also equipped with a fire pump,and a jockey pump and are tied into the fire alarm system.

Each sprinkler head is held closed independently by heat-sensitive seals.

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6.1 Fire sprinkler

Figure 13:

Figure 14:

These seals prevent water flow until a design temperature is exceeded atthe individual sprinkler heads. Each sprinkler activates independently whenthe predetermined heat level is reached. The design intention is to limitthe total number of sprinklers that operate, thereby providing the maximumwater supply available from the water source to the point of fire origin.

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7. Elevators

7 Elevators

An elevator is a transport device used to move goods or people vertically. InCommonwealth English, elevators are more commonly called lifts. Becauseof wheelchair access laws, elevators are often a requirement in new buildingswith multiple floors.

Elevators are of two types, hydraulic and traction. The hydraulic elevatorconsists of a cab attached to the top of a hydraulic jack similar to a jackused for a car lift in a service station. The hydraulic jack assembly normallyextends below the lowest floor and is operated by a hydraulic pump andreservoir, both of which are usually located in a separate room adjacent tothe elevator shaft, as shown in Figure. Hydraulic elevators are the typegenerally used in single-family residences. The second type is the tractionelevator. This is the system that is most commonly associated with elevators.The traction system consists of a cable that is connected to the top of thecab and is operated by an electric motor located in a penthouse above theelevator shaft, as shown in Figure.

Figure 15:

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8. Intercom

8 Intercom

An intercom is an electronic communications system within a building orgroup of buildings. Intercoms are generally composed of fixed microphone/speakerunits which connect to a central control panel. A small home intercom mightconnect a few rooms in a house. Larger systems might connect all of therooms in a school or hospital to a central office. Intercoms in larger buildingsoften function as public address systems, capable of broadcasting announce-ments. In many schools, tones signaling the change of classes are soundedover the intercom, taking the place of the electromechanical bells used inolder schools. Intercom systems can also be found on passenger and rapidtransit trains.

8.1 Types of intercoms

8.1.1 Two wire

Two-wire Intercom systems are widely used in TV stations and outside broad-cast vehicles such as those used at sporting events or entertainment venues.There are essentially two different types of intercoms used in the televisionworld, Two-Wire party lines or Four-Wire matrix systems. In the beginningof TV broadcasting stations would simply build their own communicationsystems using old phone equipment, however, today there are several man-ufacturers of off the shelf systems. From the late 70s until the mid 90sthe two-wire party line type systems were the most popular primarily dueto the technology that was available at the time. They used a central powersupply to drive external stations or belt packs. These systems were veryrobust and simple to design, maintain and operate but had limited capacityand flexibility as they were usually hardwired. This meant that a user onthe system could not choose who to talk to, rather, they were always talkingto the same person or group of people until the system was reconfigured toallow communication with a different group of people.

8.1.2 Four wire

Four-wire In the mid-90s Four-Wire technology started gaining more promi-nence due to the technology getting cheaper and smaller. Four-wire technol-ogy had been around for quite some time but was very expensive to imple-ment and usually required a large footprint in the physical TV Plant thuswas only used at very large stations or TV networks. Also, the large phys-ical size made it virtually impossible to use on a mobile platform such asan outside broadcast vehicle. The term four-wire comes from the fact that

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9. Air conditioning

the system uses a transmit pair and a receive pair for the audio to and fromthe intercom; four wires. That said, in a modern four-wire system there areactually six wires; two for data or a data pair that make 5 and 6, neverthelessthe phrase has stuck and this is the accepted term for these systems today.One major advantage of these systems vs. the two-wire systems is the abilityto do point to point communication at will.

Figure 16:

9 Air conditioning

9.1 Introduction

In the broadest sense air conditioning can refer to any form of cooling, heat-ing, ventilation or disinfection that modifies the condition of air, typicallyfor thermal comfort. The more common use of air conditioning is to meancooling and often dehumidification of indoor air, typically via refrigeration.

An air conditioner is an appliance, system, or mechanism designed toextract heat from an area using a refrigeration cycle. The most commonuses of modern air conditioners are for comfort cooling in buildings andtransportation vehicles.

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9.2 Air conditioning application

9.2 Air conditioning application

9.2.1 Comfort application

Comfort applications aim to provide an indoor environment that remainsrelatively constant in a range preferred by humans despite changes in externalweather conditions or in internal heat loads.

Low-Rise Residential buildings including single family houses, duplexes,and small apartment buildings

Hi-Rise Residential buildings such as tall dormitories and apartmentblocks

Commercial buildings which are built for commerce, including offices,malls, shopping centers, restaurants, etc.

Institutional buildings includes hospitals, governmental, academic, andso on.

Industrial spaces where thermal comfort of workers is desired.

In addition to buildings, air conditioning can be used for comfort in awide variety of transportation including land vehicles, trains, ships, aircraft,and spacecraft.

9.2.2 Process application

Process applications aim to provide a suitable environment for a process beingcarried out, regardless of internal heat loads and external weather conditions.Although often in the comfort range, it is the needs of the process thatdetermine conditions, not human preference. Process applications include:

Hospital operating theatres in which air is filtered to high levels toreduce infection risk and the humidity controlled to limit patient dehy-dration. Although temperatures are often in the comfort range, somespecialist procedures such as open heart surgery require low tempera-tures (about 18 C, 64 F) and others such as neonatal relatively hightemperatures (about 28 C, 82 F).

Cleanrooms for the production of integrated circuits, pharmaceuticalsand the like in which very high levels of air cleanliness and control oftemperature and humidity are required for the success of the process.

18

9.3 Basic principle of air conditioning

Facilities for breeding laboratory animals. Since many animals nor-mally only reproduce in spring, holding them in rooms at which condi-tions mirror spring all year can cause them to reproduce year round.

Aircraft air conditioning. Although nominally aimed at providing com-fort for passengers and cooling of equipment, aircraft air conditioningpresents a special process because of the low air pressure outside theaircraft.

Data processing centers Textile factories Physical testing facilities Plants and farm growing areas Nuclear facilities Mines Industrial environments Food cooking and processing areas

In both comfort and process applications the objective to not only controltemperature, but also humidity, air movement, and air quality.

9.3 Basic principle of air conditioning

In the vapor-compression refrigeration cycle, heat is transferred from a lowertemperature source to a higher temperature heat sink. Heat naturally flowsin the opposite direction, and due to the second law of thermodynamics workis required to move heat from cold to hot. A food refrigerator or freezer worksin much the same way; it moves heat out of the interior into the room inwhich it stands.

A diagram of the refrigeration cycle: 1) condensing coil, 2) expansionvalve, 3) evaporator coil, 4) compressor.

19

10. Local area network (LAN)

1

2

3

Figure 17:

10 Local area network (LAN)

A local area network (LAN) is a computer network covering a local area, likea home, office, or group of buildings. Each node or computer in the LAN hasits own computing power but it can also access other devices on the LANsubject to the permissions it has been allowed. These could include data, themore expensive devices / less used resources that it would be impractical tohave multiple copies of, and the ability to communicate or chat with otherusers in the network.

Although switched Ethernet is now the most common data link layerprotocol (OSI 7-Layer Model), and IP as a network layer protocol, many dif-ferent options have been used (see below), and some continue to be popularin niche areas. Smaller LANs consist of a few switches typically connectedto each other and with one connected to a router, cable modem, or DSLmodem. A traditional model of access, distribution, and core switches waspopularized by Cisco Systems and has been in use for many years.

Larger LANs are characterized by distributing Ethernet traffic roles withinthe network. Each layer aggregates traffic of the layer below it and will typi-cally maintain redundant links with switches capable of quality of service andspanning tree protocol to prevent loops and the recovery of failed uplinks.

20

11. Home heating system

11 Home heating system

11.1 Types of home heating systems

11.1.1 Traditional Furnaces

A furnace draws air from the house into a ductwork system, taking it to anarea where it is warmed before being delivered back to living spaces. Newerfurnaces use blowers to recirculate the warmed air. A furnace may be fueledwith gas, electricity, oil, or even coal or wood.

Circulating air is drawn through a filter that helps rid the house of dustand other particles.

Gas and oil furnaces have a pilot light that warms a heat exchangeunit, which in turn warms the air before it is circulated back throughthe house. These furnaces have a flue where exhaust gases vent to theoutside.

An electric furnace uses heating strips, or elements, to warm the air. A wood or coal furnace has a sealed firebox where the fuel is burned,and a heat exchanger where air is warmed before delivery.

Metal vents that allow warmed air to escape from the system and intothe house are usually found in the floors or on walls in living areas.

11.1.2 Electric Heat Pump

Heat pumps work by shuffling heat from one place to another. They alsoserve as air conditioners during warm weather. Heat pumps extract warmthfrom outdoor air, from ground or surface water, or from the earth. The air iswarmed more by the system if necessary, then circulated through the house.

11.1.3 Radiant Baseboard Heat

Baseboard heaters are often visible as long, metal units with electrical ele-ments inside. Each unit has its own control, which may be marked in incre-ments from low-to-high, but will not show the rooms current temperature.

21

11.1 Types of home heating systems

11.1.4 Radiant Ceiling or Floor Heat

Radiant systems warm objects in much the same way as the sun does. Noblowers are used. Electric radiant elements are installed in floors or ceilings.In the examples Ive seen, each area has a dial control similar to the onesthat operate baseboard heating units. Heating elements can also be installedin walls, but that location is less common.

Hydrolic Heating is another type of radiant heat, where hot water flowsthrough tubes under the floor or through units that resemble baseboardheaters.

22

CONTENTS

EEE 314 Lecture 5

Prepared by: Md. Itrat Bin Shams (Sanin)

Contents

1 LAN (Local Area Network) 11.1 Definition of LAN . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 LAN access method . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Carrier sense multiple access collision detect (CSMA/CD) 21.2.2 Token passing . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Some other informations . . . . . . . . . . . . . . . . . . . . . 21.4 LAN Transmission Methods . . . . . . . . . . . . . . . . . . . 2

1.4.1 Unicast transmission . . . . . . . . . . . . . . . . . . . 31.4.2 Multicast transmission . . . . . . . . . . . . . . . . . . 31.4.3 Broadcast transmission . . . . . . . . . . . . . . . . . . 3

1.5 LAN Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . 31.6 LAN Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Intercom 52.1 General Information . . . . . . . . . . . . . . . . . . . . . . . 52.2 Some terms related to intercoms . . . . . . . . . . . . . . . . . 62.3 Classification of Intercoms . . . . . . . . . . . . . . . . . . . . 7

2.3.1 Full duplex intercom . . . . . . . . . . . . . . . . . . . 72.3.2 ClearCom type intercom systems . . . . . . . . . . . . 72.3.3 RTS TW Intercom . . . . . . . . . . . . . . . . . . . . 72.3.4 Matrix intercoms . . . . . . . . . . . . . . . . . . . . . 72.3.5 Wireless Intercom System . . . . . . . . . . . . . . . . 7

1 LAN (Local Area Network)

1.1 Definition of LAN

LAN can be defined as high speed data network. It covers a small geographicnetwork. LAN can be used to connect several computers, printers, computeraccessories, other devices etc. It helps many users to access one device (sayone printer is used by many computers). It also serves users to exchangefiles,emails etc.

1

1.2 LAN access method

1.2 LAN access method

In a LAN there are many users. It is possible that two users may want toaccess same device at a time. It will certainly create a problem as the devicecan be accessed by one user at a time. Two methods are used to preventthis.

1.2.1 Carrier sense multiple access collision detect (CSMA/CD)

Here collision detect sensing is applied. It works as this: suppose two usersare sending data at the same time. If a collision occurs, it is sensed by oneuser. That user then waits for a random while. Then he sends the dataagain. In most of the cases collision will not occur again. It is because ofthe network connection. It is customary that more the number of the users,more will be the number of collisions. So if a LAN has many users, then itllcertainly become slow.

1.2.2 Token passing

Here a token is passed from device to device. If a device wants to send data,it has to wait for token to be received. The main advantage of this methodis this that it is deterministic. It means it is possible to calculate maximumtime it will take for a device to send data.

1.3 Some other informations

In CSMA/CD we can have half duplex mode of communication. Here oneuser can send a data but cannot listen to the network at the same time. Ifhe wants to listen the network he must stop sending the data. It is morelike a walkie-talkie. Only one person can talk and other can only listen in aparticular time.

When switches are introduced, we can have full duplex mode of operation.Here a user can send and receive data from the network simultaneously. Itis like regular phones, where we can talk and listen at the same time.

1.4 LAN Transmission Methods

There are three ways for this. They are,

2

1.5 LAN Topologies

1.4.1 Unicast transmission

In this type of transmission one user communicates with another user. It islike sending email to one person.

1.4.2 Multicast transmission

In this type, one user sends data to the network. It is then copied and sentto many users. It is like sending emails to many persons.

1.4.3 Broadcast transmission

In broadcast transmission, a persons data is sent to the network and a lotof copies of it is made. After this it is sent to all the users in that network.

1.5 LAN Topologies

LAN topologies is the manner in which network devices are connected. Thereare four common LAN topologies. They are: bus, ring, star, and tree.

1. BUS Topology: A bus topology is a connection scheme where all thedevices are connected to a one common bus. All the necessary data aresend to it firstly and then to other destinations.

Figure 1: Bus Topology

2. Ring Topology: In ring topology all the devices are connected in se-ries to form a ring network. Here data can be sent in unidirectionalmethod. If one computer wants to access another, it got to go throughall other computers connected between them.

3. Star Topology: In star topology all the users are connected to onecommon master. If any user wants to send data to other he has to gothrough the master.

3

1.6 LAN Devices

Figure 2: Ring Topology

4. Tree Topology: In tree topology, branches are formed. Here hierar-chy levels are well defined.

1.6 LAN Devices

1. Repeater: A repeater is a device that is used to interconnect twodevices. It is possible that wires used to connect two devices may belong or of bad quality. It is expected that signals traveling throughthem may be deteriorated. Repeaters are used to amplify, restore thesignal to its original format.

2. Hub: A hub is a device that connects multiple user stations, each bya dedicated cable. Electrical interconnections are made inside the hub.Hubs are used to create a physical star network while maintaining thelogical bus or ring topologies of the LAN.

3. LAN Extender: A LAN extender is used to connect to a more broadnetwork. Its function is to sequence and filter data to be sent.

4

2. Intercom

Figure 3: Star Topology

Figure 4: Repeater

2 Intercom

2.1 General Information

Intercom is a private telecommunication system that allows typically two ormore persons to communicate with each other like a telephone. Two wired

5

2.2 Some terms related to intercoms

Figure 5: LAN Extender

intercom system can be used as an intercom.

2.2 Some terms related to intercoms

Point-to-Point (P-P): Point-to-Point can be defined as one-way com-munication between two intercom stations. Receiving station mustpress a key to listen to sending station signal.

Party Line (PL): Party-line communication is a communication be-tween two or more stations in full duplex mode. Each station has toactivate the listen key to the desired party line to listen and the talkkey to talk. Any station can be added and subtracted from a party lineby activating talk and listen keys.

IFB: IFB means Interruptible Foldback. Here user is interrupted byone audio source while listening another source.

IRF: IRF stands for Interrupted Return Feed. It is same as IFB.

6

2.3 Classification of Intercoms

Tally: Tally is a signal to indicate a particular purpose. The ringingsound of a telephone is a tally.

2.3 Classification of Intercoms

There several types of intercoms. Some are,

2.3.1 Full duplex intercom

In a full duplex intercom system the users can communicate with each otheron both directions without any specific control (like pushing buttons as inwalkie-talkie.).

2.3.2 ClearCom type intercom systems

This type of intercom allows users to communicate in two directions betweenanyone on the line on the basis that everyone hears everything.

2.3.3 RTS TW Intercom

The TW (two wire) Intercom System is a two-wire conference- line communi-cations system that allows up to 50 user stations to connect across a commonline (also called a channel).

2.3.4 Matrix intercoms

A matrix intercom makes the user to have great power and flexibility. Thisis largely because a matrix intercom consists of cross-points that allow anyintercom input to be routed to any intercom output.

2.3.5 Wireless Intercom System

It is a general intercom system that has wireless privilege.

7

EEE 314

Electrical Services Design

Conduit Layout Lecture 1

Prepared by: Md. Itrat Bin Shams (Sanin)

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 2

Symbols used in fittings and fixtures and in conduit layout: Symbol Description Fittings and Fixture Conduit Layout

Wall Bracket Light at Lintel Level

2-Pin 5A Socket at SB Level

3-Pin 5A/15A Socket at Skirting Level

2-Pin 5A Socket at Table Height

3-Pin 5A Socket at Lintel Level

2-Pin 5A Socket at Skirting Level for TV

S

S

T

S

S

SL

TS

ST

15

L

SS

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 3

2-pin TV Antenna Socket

Same

Push Button

Same

Calling Bell or Buzzer

Same

Switch Board Concealed

Same

20A SP MCB At Skirting Level

Same

Fluorescent Wall Light Fitting

L

M

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 4

4-point Chandelier Light Fitting

Ceiling Light Fitting Type k

Same

Meter Board

Same

Distribution Board

Same

Exhaust Fan

Same

Ceiling Fan

F

K

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 5

Telephone Grommet

Same

Some Access Symbols: Symbol Conduit Layout Symbol

Concealed Conduit

Concealed Conduit Going Down

PVC Pipe Running through Floor

Miniature Circuit Breaker

Conduit Going up

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 6

Example 1: Fittings and Fixtures layout:

A1

1

Switch Board Concealed

Wall Bracket Light at Lintel Level

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 7

Conduit Layout:

L

1

LWall Outlet at Lintel Level

C1

C1 = 2 X 1.5 mm2

SB 1

A 1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 8

Example 2: Fittings and Fixture Layout:

A1 1

Switch Board Concealed

Wall Bracket Light at Lintel Level

A2

F1

Ceiling Fan

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 9

Conduit Layout:

L

1

L F

FCeiling Fan Outlet

Concealed Conduit

Conduit Going Down

SB 1

R

A 2

F 1

C1 C1

C3

A 1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 10

Example 3: Fittings and Fixture Layout:

A1 1

Switch Board Concealed

Wall Bracket Light at Lintel Level

A2 F1

Ceiling Fan

ST1 C1

TV1

TS1

Two Pin TV Antenna Socket

Two Pin 5A Socket at Table Height

Two Pin 5A Socket at Skirting Level for TV

ST

TS

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 11

Conduit Layout:

L

1

L F

SB 1

R

L 3

F 1

C2 C1

C6

LT

S

S

T

Socket Outlet at Skirting Height

Socket Outlet at Table Height

ST TS 1 1

C1

C2 C1

A A C 1 2 1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 12

Example 4: Fittings and Fixture Layout:

A11

A2 F1

C1 TV1

SS1

2A3

SS3

F2

Two Pin 5A Socket at SB Level

SS2

TS1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 13

Conduit Layout:

L

1

L

S

S

S

S

L

2

F

L

F

C1

C3 C7

C2

C1

C2

C1 C1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 14

Switch-Board Connection Diagram:

SB 1 SB 2

A A C F SS SS TS 1 2 1 1 1 2 1

A F SS 3 2 3

2 X 1.5 mm2

R R

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 15

Assignment:

A1

1

A2 F1

C1

TVSS1

2

SS3

F2

TS1

SS2

L2 L1

C2A3

C2

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 16

Practice Section: Draw Conduit Diagram for Example 1:

Draw Conduit Diagram for Example 2:

L

1

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 17

Draw Conduit Diagram for Example 3:

Draw Conduit Diagram for Example 4:

L

1

L F

L

1

L F

LT

S

Prepared by: Md. Itrat Bin Shams (Sanin) Lecturer, EEE, BUET.

EEE 314: Drawing Lecture 1 18

L

1

L

S

S

S

S